The invention relates to the field of the information storage.
At present, most of storage devices, such as magnetic discs, compact discs, etc., record data in a two-dimensional manner, with a lower storage capacity being from about 10 GB up to about 35 GB and a slower access rate being not more than 1 MB/s, so as to be not by far able to satisfy the needs for information storage, information transmission, and information processing in the future. The data storage of a high density has been all along an indispensable key field in the development of the information technology and the computer technology. By the year of 2005 when the network of new kind and the multimedia of third generation appear, for any computer, at least 100 GB of the external storage capacity and at least 40 MBps of the data transfer rate will be demanded. But unfortunately, existing various kinds of external storage devices can not satisfy these demands, even DVD compact disc systems which have just entered markets are far away from this object. The only way solving these problems is to use new principles, new technologies, and new materials in order to develop a storage technology and system of a new generation having a high density and a high speed.
The three-dimensional storage technology based on the holographic storage have a number of good properties such as a large capacity of data storage, a short access time and a high data transfer rate. The three-dimensional holographic storage technology records and read information as two-dimensional holographic pages, and data are record in parallel through the volume of the crystal rather than localized on a surface or thin film as in traditional storage. In this way, a high-density (in the order of 1013 bit/cm3 or greater) information storage could be realized by this kind of three-dimensional optical storage, with a high data transfer rate being equal or more than 109 bits/s and a readout time for one data page (up to 106 bits per page) being smaller than 100 xcexcs. At present, however, in many prior three-dimensional storage configurations, so called 90xc2x0-configuration is widely used and the green light is used as the readout beam. Therefore it is difficult to guarantee against the fixing time and it is not ease to miniature the system.
An object of the invention is to provide a three-dimensional optical storage systems, which could realize a high-density information storage with a short writing and read access time, and to resolve the problem of the information fixing time to meet the ever-increasing need for the information storage of multimedia data and to adapt to the future need of a high-speed information development.
The only-readable three-dimensional optical storage of the invention consists of two systems: one is the writing system which includes a computer, a beam splitter, a precise rotary table, a light-source for writing, lenses, a spatial light modulator, a spatial filter, mirrors, a photorefractive crystal (such as doped or doubly doped LiNbO3 or LiTaO3) and a charge-coupled device (CCD); another one is the readout system which includes a computer, a precise rotary table, a slit, a phase-mismatch adjustor, a light source for readout, a photorefractive crystal (such as doped or doubly doped LiNbO3 or LiTaO3), lenses and CCD. The photorefractive crystal used in the readout system is the one in which the information has been recorded by way of the writing system.
The intersect angle 2 xcex8 of the two writing beam from the lens 106 and mirror 108 is within the range of 10xc2x0xcx9c35xc2x0; the angle between the light from the phase-mismatch adjustor 202 and the diffracted light from the photorefractive crystal 204 to the lens 207 is 180xc2x0-2xcex1, the relationship between xcex1 and xcex8 is xcex wsin xcex8=xcexr sin xcex1, where xcexw and xcexr are the wavelengths of writing light and readout light, respectively.
The spatial light modulator is used to show under the control of a computer the information which will be stored, the photorefractive crystal is fixed onto the precise rotary table which is controlled by the computer to get to any desired angle, and the CCD collects the image to the computer for further processing. The phase-mismatch adjustor is used to compensate for the phase mismatch when the red light is used for read out the stored images, which were recorded by the green light. The phase-mismatch adjustor is an irregular double-convex lens, with the transverse focus length range of 50xcx9c400 mm and the longitudinal focus lens range of 300 mmxcx9c+∞
The implementation mode of the of the invention is: using the photorefractive crystals (doped or doubly doped LiNbO3 or LiTaO3) as the three-dimensional holographic storage optical disc materials; using the green light (wavelength 532 nm) from the solid-state laser to write the information in the crystal according to the holographic way through the photorefractive effect of the crystals in the transmission configuration; and using the red light (typical wavelength xcx9c670 nm) from the semiconductor laser as the readout beam; where the phase-mismatch adjustor is a specially designed irregular double-convex lens, and the dynamically differential technique is used to encode and decode the computer files.